EP1218004B1

EP1218004B1 - 5-methyl indirubin for use in the treatment of human solid tumors

Info

Publication number: EP1218004B1
Application number: EP00922625A
Authority: EP
Inventors: Gerhard Prof.Dr. Eisenbrand; Heinz Herbert Fiebig; Weici Tang; Doris Marko; Ralph Hössel
Original assignee: Individual
Current assignee: FIEBIG, HEINZ HERBERT
Priority date: 1999-04-12
Filing date: 2000-04-11
Publication date: 2009-04-08
Anticipated expiration: 2020-04-11
Also published as: BR0009771A; DE60041974D1; AU775633B2; JP2002541189A; CN1378447A; MXPA01010436A; AU4294900A; CA2369626A1; CA2369626C; WO2000061124A3; EP1218004A2; WO2000061124A2; US6664285B1; ATE427746T1

Abstract

The present invention relates to the use of cell membrane penetrating indigoid bisindole derivatives for the manufacture of a medicament for the treatment of human solid cancers.

Description

The present invention relates to the use of a cell membrane penetrating indirubin bisindole derivative for the manufacture of a medicament for the treatment of human solid cancers.
Indigoid bisindoles comprise a spectrum of natural dye stuffs. Many of these can be obtained from plants. Accordingly, indirubin, indigo and isoindigo are natural products which can be obtained from different plants: namely, Baphicacanthus cusia (Acanthaceae), Indigofera suffruticosa (Fabaceae), Isatis indigotica (Brassicaceae) and others. Indican, a glycoside which is found in plants, gives glucose and 3-hydroxyindole due to acidic or enzymatic hydrolysis. 3-Hydroxyindole is converted by air-oxidation into indigo and its isomers. Indigo naturalis (Chinese: quingdai) is the natural blue dye obtained from plant material, e.g. lsatis indigotica (Brassicaceae). Indirubin, an isomer of indigo, can be found in Indigo naturalis in an amount of up to 60% (Falbe J. & Regitz M., Römpp Chemie Lexikon (1992), 9. Aufl., Stuttgart, Georg Thieme Verlag). It occurs also in Isatis tinctoria in an amount of up to 5% which is indigenous to Central Europe (Gelius R., Z. Chem., 20, (1980), 340-341). Derivatives of indirubin are known for a long time as dyes of low persistence.
Indigo naturalis is reported to be used in traditional Chinese medicine as a haemostatic, anti-pyretic, anti-inflammatory and sedative agent in the treatment of bacterial and viral infections. Antileukemic effects of Indigo naturalis have also been reported, with indirubin being the effective principle (Ji X. et al., Acta Pharm. Sin., 16, (1981), 146-148; Gan W. J. et al., J. Hematol., 6, (1985), 611-613). In spite of its anti-leukaemic activity, however, indirubin dissolves only poorly in water and is therefore not readily resorbed. Recently, the antileukemic activity of some better soluble indirubin derivatives has been reported (Ch. Li et a., Bull. Chem. Soc, Jpn. 69, 1621-1627 (1996)).
Derwent Abstract XP-002164029 describes inter alia lower alkyl indirubins which, however, are N-alkyl indirubins, as well as lower alkyl indigos and lower alkyl isoindigotins. The respective compounds are said to exhibit anti-tumor activity against Walker 256 carcinosarcoma and Lewis-Lung carcinoma in rodents. Derwent Abstract XP-002164030 describes indirubin derivatives which are useful as anti-tumoral agents. Wu K. et al.:"Potential antileukemic agents systhesis of derivatives of indirubinindigo, and isoindigotin", Acta Pharmaceutica Sinica, Beijing, CN, vol. 20, no. 11, 1985, pages 821-826, describes the study of the role of N₁-substitution and connecting position of two indole rings in the anti-tumor activity, by synthesizing two N₁-substituted and one N₁,N₁-bis-substituted derivatives of indirubin, wherein it was found that the N₁-substitution caused loss of anti-tumoral activity in Walker 256 carcinoma, wherein the bis-substituted derivative showed some activity. Li L. et al.:"Chemical studies of strobilanthes cusia", Acta Pharmaceutica Sinica, Beijing, CN, vol. 28, no. 3, 1993, pages 238-240 describes the isolation of inter alia an indirubin compound from the whole plant of Strobilanthes cusia and its chemical and biological characterization, resulting in the finding that said indirubin derivative showed some anti-tumor activity. "CDK inhibition and cancer therapy", Current Opinion in Genetics and Development, Vol. 9, Nr. 1, pages 104-111, describes in general the CDK inhibition and its role, in particular in association with cancer.
However, indigoid bisindole or its derivatives have never been investigated with respect to solid tumors, in particular human solid tumors, and furthermore, the problem of the poor solubility resulting in a poor resorption has not been sufficiently solved yet.
Thus, the technical problem underlying the present invention is to provide new active substances which can be used in the treatment of human solid tumors and metastasis thereof. Furthermore, the resorption of said substances should be improved in order to improve their in vivo anti-tumor activity.
The solution to the above technical problem is achieved by the embodiments characterized in the claims.
In particular, the present invention relates to the use of a cell membrane penetrating indirubin derivative for the manufacture of a medicament for the treatment of human solid tumors and metastasis thereof wherein the indirubin derivative is selected from 5-methyl indirubin represented by the following formula (I):
wherein the solid tumors are selected from mammary carcinoma, melanoma, large-cell lung carcinoma, small-cell lung carcinoma, lung adenocarcinoma, colon carcinoma, bladder carcinoma, ovarian carcinoma, pancreatic carcinoma, renal carcinoma, prostatic carcinoma and melanomas.
The above indigoid bisindole derivatives can also be employed in the form of their physiologically acceptable salts. Furthermore, the indigoid bisindole
derivatives according to the present invention may also be chemically coupled to masking agents as described e.g. in German patent application DE-A-38 27 488 which function to carry the anti-tumor active substances to the tumor.
In the following, the indirubin derivative selected from 5-methyl indirubin according to the present invention is also addressed to as "anti-tumor active compound according to the present invention".
According to the present invention the terms "cell membrane penetrating" and "cell resorbable" mean the ability of the indirubin derivative to be taken up by the tumor ceil through the cellular membrane.
The above identified indirubin derivative of the present invention can be formulated into pharmaceutical compositions which contain optionally a pharmaceutically acceptable carrier and/or diluent. Said pharmaceutical compositions can be applied e.g. orally, topically, intravenously, intraperitoneally, subcutaneously and rectally in pharmaceutically effective amounts.
One general problem in the field of pharmacology is the formulation of pharmaceutically active substances in pharmaceutical compositions which can be applied to a human body. Since most physiological fluids are waterbased, the pharmaceutically active substances should be soluble in water and/or a water mixable solvent wherein the latter of course has to be physiologically acceptable in small concentrations, such as ethanol. Furthermore, pharmaceutically active substances which are taken orally have to be resorbed into surface of the human body - including the gastrointestinal mucous membrane- or, in case of an application via syringe, e.g. intraperitoneal or intravasal, have to be resorbed through the cellular membranes of the of destination cells, specifically into the tumor cells.
According to the present invention it has been found that in case of the indirubin derivative according to the present invention, a good solubility is not the only prerequisite guaranteeing a good anti-tumor activity in vivo as it will become apparent by the Examples and Comparative Examples shown below. An important factor for the anti-tumor activity of indirubin derivatives is their ability to penetrate the cellular membranes of the tumor cells. Cellular membranes are composed of lipids and compose a rather non-polar medium. Therefore, substitution with extremely polar groups such as the sulfonate group on the one hand improves the water solubility of a compound but on the other hand hinders or even prohibits the resorption of anti-tumor active substances into a tumor cell. Thus, anti-tumor active substances which show good anti-tumor activities under certain in vitro conditions, have to be rejected because of not showing any activity when tested using intact cells or in vivo.
Therefore, in the following Examples the testing of the anti-tumor active substances are tested by in vitro tests using intact tumor cells and, additionally, in vivo tests. Furthermore, a comparison of the activity test results and the tests evaluating the ability to penetrate cellular membranes shows that indigoid bisindole compounds which exhibit a good cell-penetrating ability also show good to excellent anti-tumor activity.
The Figures show:

Fig. 1 is a graph which shows the development of the relative tumor volume with time during chemotherapy of LXFL 529/17 with indigoid bisindole derivatives (compounds according to Examples 1, 4 and 6). The anti-tumor active substances were applied intraperitoneally to nude mice in doses and according to the schedule as described below in Table 4. Compared to the vehicle control, all compounds significantly inhibited the tumor growth.
Fig. 2 is a graph which shows the relative body weight change of the tested nude mice with time during chemotherapy of LXFL 529/17. 5-Methylindirubin (Example 5) at a dosage of 100 mg/kg up to 300 mg/kg showed very high anti-tumor activity (Fig. 1 and Fig. 3) without any significant reduction of body weight (Fig. 2 and Fig. 4) thus demonstrating high anti-tumor activity without significant toxicity.
Fig. 3, Fig. 5 and Fig. 7 are graphs which show the relative tumor volume versus the time during the chemotherapy of LXFL 529/17 with other indigoid bisindole derivatives (compounds according to Examples 8, 9, 10 and 14).
Fig. 4, Fig. 6 and Fig. 8 are graphs which show the relative body weight change of the tested nude mice with time during chemotherapy of LXFL 529/17 using said other indigoid bisindole derivatives.

The present invention is explained in detail by the following example and comparative examples by which also further advantages of the present invention will become apparent. Only Example 6 is in accordance with the present invention, while Examples 1 to 5 and 7 to 14 are for illustrative purposes, thus indicated as Reference Examples.

1. Synthesis of indigoid bisindole derivatives

Example 1 (Indirubin) (Reference Example)

To a solution of 0.42 g (2.4 mmol) of indoxyl acetate in 20 ml methanol under argon 0.35 g (2.4 mmol) of isatin and 0.55 g (5.2 mmol) of sodium carbonate are added. The mixture is stirred for 30 min at ambient temperature. After 24 h standing at ambient temperature, the reaction mixture is filtered off. The precipitate is washed with little methanol and water until the filtrate shows a neutral pH. Residual water is removed by storage in an evacuated exsiccator over potassium hydroxide, Recrystallisation from ethanol or pyridine gives deep purple crystals (Russell G.A., Kaupp G. (1969), J. Am. Chem. Soc., 91, 3851-9, modified).
Yield: 0.51 g (81%), fine, deep-purple needles, Fp: 341-343°C
CHN-analysis: (C₁₆H₁₀N₂O₂); MW: 262.26 g/mol;
calc.: 73.3% C, 3.8% H, 10.7% N;
found: 73.2% C, 4.0% H, 10.6% N
mass spectrum: m/z = 262: (M⁺, 100%), 234: (43%), 205 (25%), 158 (3%), 131 (4%), 103 (7%), 76(3%)
¹H-NMR and ¹³C-NMR-spectrum are in accordance with the proposed structure. IR-spectrum: 3340 cm^-1: v (N-H), 1.710 cm^-1: v (3'-C=D), 1650 cm^-1: v (2-C = O), 1590 cm^-1: v (C=C, aryl), 1450 cm^-1: v (C = C, aryl), 745 cm^-1; v (aryl with four neighbouring H-atoms).
UV/Vis-spectrum (DMSO): 290 nm, 363 nm, 383 nm (shoulder), 551nm
Essentially the same synthetic procedure was applied for the following Examples 2 to 9, 12, 13 and Comparative Examples 1 and 2:

Example 2 (5-Iodoindirubine) (Reference Example)

Yield: 80%, fine, deep-purple needles, Fp: 334-335 °C (decomposition);
CHN-analysis (C₁₆H₉IN₂O₂); MG = 388.16 g/mol;
calc.: 49.5% C, 2.3% H, 7.2% N;
found.: 49.7% C, 2.5% H, 7.1% N;
Mass spectrum: 388 (M⁺, 100%), 360 (3%), 269 (9%), 261 (6%), 233 (16%), 205 (16%), 128 (1 %);
¹H-NMR- and ¹³C-NMR-spectrum are in accordance with the proposed structure. UV/Vis-spectrum (DMSO): 370 nm, 386 nm (shoulder), 555 nm.

Example 3 (5-Bromoindirubin) (Reference Example)

Yield: 70%, fine, deep-purple needles;
CHN-analysis (C₁₆H₉BrN₂O₂); MG = 341.16 g/mol,
calc.: 56.3% C, 2.7% H, 8.2% N;
found 56.4% C, 2.7% H, 8.2% N;
Mass spectrum: 342(M⁺, 100%), 340 (M⁺, 99%), 314 (18%), 262 (64%), 233 (34%), 205 (81%), 177 (10%);
¹H-NMR- and ¹³C-NMR-spectrum are in accordance with the proposed structure.

Example 4 (5-Chloroindirubin) (Reference Example)

Yield: 95%, fine, deep-purple needles;
CHN-analysis (C₁₆H₉ClN₂O₂); MG = 296.70 g/mol;
calc.: 49.5% C, 2.3% H, 7.2% N;
found: 49.7% C, 2.5% H, 7.1% N;
Mass spectrum: m/z = 296 (M⁺, 100%), 268 (39%), 239 (8%), 233 (35%), 205 (50%), 177 (7%), 153 (6%), 137 (7%), 77 (7%), 120 (4%), 102 (6%), 77 (7%).
¹H-NMR- and ¹³C-NMR-spectrum are in accordance with the proposed structure.

Example 5 (5-Fluoroindirubin) (Reference Example)

Yield: 92%, fine, deep-purple needles;
CHN-analysis (C₁₆H₉FN₂O₂), MG = 280.25 g/mol,
calc.: 68.6% C, 3.2% H, 9.9% N;
found: 68.0%C, 3.2% H, 9.9% N;
Mass spectrum: m/z = 281 (M⁺ +H⁺, 19%), 280 (M⁺, 100%), 252 (73%), 223 (32%), 176 (6%), 140 (7%), 121 (13%), 94 (4%), 76 (12%), 77 (7%), 57 (4%), 44(15%).
¹H-NMR- and ¹³C-NMR-spectrum are in accordance with the proposed structure.

Example 6 (5-Methylindirubin) (in accordance with the invention)

Yield: 92%, fine, deep-purple needles;
CHN-analysis (C₁₇H₁₂N₂O₂), MG = 276:28 g/mol,
calc.; 73.9% C, 4.4% H, 10.1% N;
found: 73.8%C, 4.3% H, 10.2% N;
Mass spectrum: m/z = 276 (M⁺, 100%), 261 (10%), 248 (47%), 247 (53%), 220 (6%), 219 (18%), 205 (7%), 171 (4%), 165 (10%), 138 (4%), 133 (15%), 104 (7%), 77 (7%);
¹H-NMR- and ¹³C-NMR-spectrum are in accordance with the proposed structure.

Example 7 (5-Nitroindirubin) (Reference Example)

Yield: 88%, fine, deep-purple needles;
CHN-analysis (C₁₆H₉N₃O₄), MG = 307.26 g/mol;
calc.: 62.5% C, 3.0% H, 13.7% N;
found: 62.4%C, 3.0% H, 13.3% N;
Mass spectrum: m/z = 307 (M⁺, 5%), 276 (10%), 262 (100%), 234 (23%), 205 (22%), 158 (6%), 131 (10), 104 (19%), 76 (12%), 50 (6%).
¹H-NMR- and ¹³C-NMR-spectrum are in accordance with the proposed structure.

Example 8 (Indirubin-3'-oxime) (Reference Example)

Indirubin-3'-oxime was synthesized by reaction of indirubin with hydroxylamine hydrochloride in a pyridine solution (Farbwerke vorm. Meister Lucius & Brüning in Hoechst a.M., Patentschrift des Reichspatentamtes Nr. 283726 (1913)). ¹³C-NMR-spectroscopy revealed the location of the hydroxyimino residue in 3'-Position (δ(C2) = 171.05 ppm; δ(C3') = 145.42 ppm; DMSO-d₆, RT)
Yield: 90 %, red crystals;
CHN-analysis (C₁₆H₁₁N₃O₂), MG = 277.30 g/mol;
calc.: 69.3% C, 4.0% H, 15.2 % N;
found: 69.0% C, 4.0% H, 14.9% N;
¹H-NMR- and ¹³C-NMR-spectrum are in accordance with the proposed structure.

Example 9 (5-Iodoindirubine-3'-oxime) (Reference Example)

Indirubin-3'-oxime was synthesized by reaction of 5-Iodoindirubine with hydroxylamine hydrochloride in a pyridine solution. ¹³C-NMR-spectroscopy revealed the location of the hydroxyimino residue in 3'-position (δ(C2) = 170.25 ppm; δ(C3') = 151.52 ppm; DMSO-d₆, RT)
Yield: 90 %, red crystals;
CHN-analysis (C₁₆H₁₀IN₃O₂), MG = 403,20 g/mol;
calc.: 47,7%C, 2,5% H, 10,4% N;
found: 47,1 % C, 2,5% H, 10,1 % N;
¹H-NMR- and ¹³C-NMR-spectrum are in accordance with the proposed structure.

Example 10 (Isoindigo) (Reference Example)

Isoindigo was synthesized by reaction of oxindole with isatin in acetic acid with addition of hydrochloric acid (Wahl A., Bayard P., Comptes Rendues Hebdomadaires des Seances de L'Academie des Sciences, 148, (1909), 716-719).
Yield: 84%, crystalline, brown substance;
CHN-analysis (C₁₆H₁₀N₂O₂), MG = 262.26 g/mol;
calc.: 73.3% C, 3.8% H, 10.7% N;
found: 73.0% C, 3.8% H, 10.9% N;
Mass spectrum: m/z = 262 (M⁺, 100%), 234 (85%), 220 (5%), 205 (18%), 190 (4%), 177 (5%), 151 (5%), 132 (17%), 103 (6%), 76 (4%), 32 (26%).
¹H-NMR- and ¹³C-NMR-spectrum are in accordance with the proposed structure.

Example 11 (Indigo) (Reference Example)

Chemical grade indigo was purchased by Fluka Chemie AG.

Example 12 (indirubin-5-sulfonamide (Reference Example)

¹H-NMR- and ¹³C-NMR-spectrum are in accordance with the proposed structure.

Example 13 (indirubin-5-sulfone(2-hydroxyethyl)amide (Reference Example)

¹H-NMR- and ¹³C-NMR-spectrum are in accordance with the proposed structure.

Example 14 (Bis(3-phenylindol-2-yl)) (Reference Example)

To a cooled solution of 2-aminobenzophenone in dichloromethane and pyridine under inert gas, a solution of oxalyl chloride in dichloromethane is dropped. After completion of the reaction, 0.5 n hydrochloric acid is added, the formed precipitate is filtrated off and washed subsequently with 0.5 n hydrochloric acid, a solution of sodium hydrogencarbonate and water, The obtained product (N,N'-bis(2-benzoylphenyl)-oxamide), zinc dust and titanium(III)chloride are suspended in dimethoxyethane and heated to reflux. After heating for 3 h, the mixture is cooled to ambient temperature and the precipitate is filtrated off and washed with ethyl acetate. The crude product is purified using column chromatography (silica gel), then dissolved in ethyl acetate and precipitated in form of white crystals by adding petrol ether.
CHN-analysis (C₂₈H₂₀N₂), MG = 384.48 g/mol;
calc.: 87.5%C, 5.2% H, 7.3% N;
found: 87.3% C, 5.3% H, 7.3% N;
¹H-NMR- and ¹³C-NMR-spectrum are in accordance with the proposed structure.

Comparative Example 1 (indirubin-5-sulfonic acid)

Yield: 76%, crystalline, deep-purple substance;
Mass spectrum: 388 (M⁺, 100%), 360 (3%), 269 (9%), 261 (6%), 233 (16%), 205 (16%), 128 (1%).
¹H-NMR- and ¹³C-NMR-spectrum are in accordance with the proposed structure.

Comparative Example 2 (Indirubin-3'-oxime-5-sulfonic acid)

Yield: 76%, crystalline, deep-purple substance;
Mass spectrum: 388 (M⁺, 100%), 360 (3%), 269 (9%), 251 (6%), 233 (16%), 205 (16%), 128 (1%).
¹H-NMR- and ¹³C-NMR-spectrum are in accordance with the proposed structure.

Table 2 summarizes the structures of the indirubin compounds of Examples 1 to 9 and Comparative Examples 1 and 2.

Table 1

Example	compound	R¹	X
1 (Ref. Ex.)	Indirubin	H
2 (Ref. Ex.)	5-Iodoindirubin	I	O
3 (Ref. Ex.)	5-Bromoindirubin	Br	O
4 (Ref. Ex.)	5-Chloroindirubin	Cl	O
5 (Ref. Ex.)	5-Fluoroindirubin	F	O
6 (Invention)	5-Methylindirubin	CH₃	O
7 (Ref. Ex.)	5-Nitroindirubin	NO₂	O
8 (Ref. Ex.)	indirubin-3'-oxime	H	NOH
9 (Ref. Ex.)	5-Iodoindirubine-3'-oxime	I	NOH
10 (Ref. Ex.)	Isoindigo
11 (Ref. Ex.)	Indigo
12 (Ref. Ex.)	Indirubin-5-sulfonamide	SO₂-NH₂	O
13 (Ref. Ex.)	Indirubin-5-sulfone(2-hydroxyethyl)amide	SO₂-NH-CH₂CH₂OH	O
14 (Ref. Ex.)	Bis(3-phenylindol-2-yl)

Comparative Examples
1	Indirubin-5-sulfonic acid Indirubin-3'-oxime-5-sulfonic	SO₃H	O
2	acid	SO₃H	NOH

2. Cellular uptake into LXFL 529L cells

The compounds of Reference Example 1, Example 6 and Reference Example 8 and Comparative Examples 1 and 2 were investigated with respect to their ability to penetrate LXFL 529L cells having the passage numbers P23 to P39. The results are shown in Table 2. The amounts of the substances taken up by the cells are given depending on the concentration of the substance within the incubation medium. The time of incubation was 2 hours in all of the experiments. Furthermore, the distribution of the substance which was taken up by the cells in the cytosol and the cellular organelles (particular) was estimated and is given in the intermediate column of Table 2. Tumor cell growth inhibition was determined by the sulfo-rhodamine B assay (SRB assay) according to Skehan et al., J. Natl. Cancer Institute 82, pages 1107 - 1112 (1990). Incubation was conducted for three days in serum containing medium. Tumor cell lines tested were a large-cell lung carcinoma xenograft line LXFL 529 L and the mammary carcinoma line MCF-7. Results are given as IC₅₀ [µM] corresponding to the concentration of compounds inducing 50 % growth inhibition, compared to vehicle treated control.

Table 2

substance	concentration of incubation	amount of substance within the cells	distribution [%]		Tumor cell growth inhibition (SR8-assay) IC₅₀ [µM]
	[µM]	[µm/mg protein]	cytosol	cellular organelles	LXFL529L	MCF7
Example 1 (Ref. Ex.)	10	0.15±0.08	7±5.7	93±5.7	9.9±0.1	4.0±2.0
Example 1 (Ref. Ex.)	20	0.20±0.08	6±1.4	94±1.4
Example 6 (Invention)	10	0.52±0.1	13±0.7	87±0.7	7.5±0.5	4.8±0.5
Example 6 (Invention)	20	0.86±0.22	6±2.8	94±2.8
Example 8 (Ref. Ex.)	10	0.16±0.01	43±14.1	57±14.1	3.0±0.5	3.3±0.4
Example 8 (Ref. Ex.)	20	0.23±0.03	44±15.6	56±15.6
Comparative Example 1	10	< 0.02	-	-	> 100	> 100
Comparative Example 1	20	< 0.02	-	-
Comparative Example 2	10	< 0.05	-	-	> 100	> 100
Comparative Example 2	20	< 0.05	-	-

The compounds according to the Example 6 and Reference Examples 1 and 8, were all taken up by the tumor cells. The ability of the compound according to Example 6 to penetrate the cellular membrane is substantially improved compared to that of the parent compound indirubin (Reference Example 1). The uptake of the compound according to Reference Example 8 is also slightly improved compared to the non-substituted indirubin

(Reference example 1)

The compounds of Comparative Examples 1 and 2 were essentially not taken up by the cells although these compound are well soluble in physiological solutions. Obviously, the sulfonate group hinders the penetration through the cellular membrane. Furthermore, referring to Comparative Example 2, this detrimental effect cannot be compensated by the introduction of an oxime group.

3. Evaluation of the anti-tumor activity

The anti-tumor activity of the compounds was evaluated via a colony-forming-assay as described e.g. by D. P. Berger et al. in Annals of ), "The clonongenic assay with human tumor xenografts, evaluation, predictive values and application for drug screening".
The experiments were conducted using various tumor cell lines, in particular mammary carcinoma (MAXF) , lung adenocarcinoma (LXFA), large-cell lung carcinoma (LXFL), small-cell lung carcinoma (LXFS), colon carcinoma (CXF), melanoma (MEXF), pancreatic carcinoma (PAXF), renal carcinoma (RXF), ovarian carcinoma (OVXF) and bladder carcinoma (BXF).
The IC₇₀-values and IC₅₀-values, respectively, define the concentration of a pharmaceutically active compound causing 70 % and 50 %, respectively, reduction of colony formation compared to the untreated control. Therefore, IC₇₀- and IC₅₀-values serve to demonstrate the anti-tumor activity of a pharmaceutically active compound wherein low IC₇₀- and/or IC₅₀-values demonstrate a superior anti-tumor activity. According to the present invention, the IC₇₀-value preferably is 20 µM or lower, more preferably 10 µM or lower.
Table 3 shows the anti-tumor activity of the compounds according to the Example, Reference Examples and Comparative Example 1. The compounds according to the Example and the Reference Examples show good to excellent anti-tumor activity against various types of tumor cell lines. The compound according to Comparative Example 1 does not exhibit an anti-tumor activity against any of the tumor lines. This behaviour is in accordance with the lacking ability of this substance to penetrate cellular membranes as demonstrated in Table 2, above.

Surprisingly, smelt variations in the substitution pattern result in remarkable changes in the anti-tumor activity profile. However, almost all compounds according to the Examples exhibit good anti-tumor activity against mammary carcinoma.

Table 3

Example	IC₅₀ [µM]	IC₇₀ [µM]	tumor xenograft
Example	IC₅₀ [µM]	IC₇₀ [µM]	type	xenograft
1 (indirubin) (Ref. Ex.)	25.3	36.6	lung large-celi	LXFL629
	2.0	6.0	mammary	MCF7X
	12.3	>30	ovarian	OVXF1353
	5.4	>30	pancreatic	PAXF736
2 (5-iodo-indirubin) (Ref. Ex.)	6.3	>30	colon	HT29X
	8.0	23	lung adeno carcinorna	LXFA526
	13,7	24.5	lung small-cell	LXFS650
	<1.0	2.5	mammary	MCF7X
	18.0	>30	pancreatic	PAXF546
3 (5-bromo-indirubin) (Ref.Ex.)	< 1.0	17.3	colon	HT29X
	2.3	14.4	lung adenocarcinoma	LXFA626
	<1.0	<1.0	mammary	MCF7X
	3.4	8.0	melanoma	MEXF514
	13.2	>30	pancreatic	HT29X
04 (5-chloro-indirubin) (Ref.Ex.)	< 1.0	<1.0	mammary	MCF7X
	17.1	26,0	melanoma	MEXF514
	3.2	8.0	pancreatic	Pax736
	11.2	24.7	renal	1220
	4,6	>30	pancreatic	PAXF546
	<1	17.3	colon	HT29X
5 (6-fluoro-indirubin) (Ref. Ex.)	<1.0	<1.0	mammary	MCF7X
	<1.0	6.1	ovarian	OVXF1353
	<1.0	1.1	pancreatic	PAXF73G
6 (5-methyl-indirubin) (Invention)	<1.0	14.4	colon	HT29X
	<1.0	1.2	mammary	MCF7X
	19.2	27.8	melanoma	MEXF514
	16.4	27.5	pancreatic	PAXF736
	1.0	>30	ovarian	OVXF1352
7 (5-nitro-indirubin) (Ref. Ex.)	<1.0	15.1	mammary	MCF7X
	4.9	>10.0	melanoma	MEXF514
8 (indirubin-3'-axima) (Ref. Ex.)	10.6	16.1	bladdar	BXF1301
	8.0	12.6	colon	CXF280
	0.9	3.4	lung adenocarcinoma	LXFA289
	7.7	9.2	mammary	MX1
	1.0	2.6	melanoma	MEXF9B9
	2.8	5.7	melanoma	MEXF515LX
9 (5-lodo-3'ooxima-indirubin) (Ref. Ex.)	4.0	5.8	bladdar	BXF1301
	10.7	16.3	colon	CXF280
	0.05	0.7	lung adenocarcinoma	LXFA289
	2.4	10.4	mammary	MCF7X
	2.6	4.9	melanoma	MEXF515LX
10 (isoindigo) (Ref. Ex.)	6.0	8.2	bladder	BXF1301
	<1.0	<1.0	colon	CXF280
	2.6	4.6	lung large-cell	LXFL529
	<1.0	<1.0	lung small cell	LXFS650
	<1.0	<1.0	mammary	MX1
	<1.0	<1.0	mammary	MCF7X
	<1.0	<1.0	melanoma	MEXF989
	<1.0	<1.0	ovarian	OVXF1355
	<1.0	<1.0	pancreatic	PAXF546
	<1.0	<1.0	pancreatic	PAXF736
	<1.0	<1.0	colon	HT29X
11 (indigo) (Ref. Ex.)	3.3	26.1	colon	HT29X
	3.6	12.3	lung adenocarcinoma	LXFA289
	3.9	16.7	ovarian	OVXF1353
13 (5-SO₂-NH-CH₂-CH₂-OH-indirubin) (Ref. Ex.)	12.0	17.3	colon	CXF280
	1.1	2.6	lung adenacarcinoma	LXFA289
	3.4	5.9	lung large-call	LXFL529
	0.6	2.1	mammary	MCF7X
	<0.1	0.4	melanoma	MEXF515LX
	0.3	0.4	ovarian	OVXF899
14 (Bis(3-phenylindol-2-yl)) (Ref. Ex.)	2.7	6.2	bladder	BXF1299
	<1.0	7.2	colon	CXF280
	1.5	3.4	colon	HT29X
	4.7	6.7	lung small-cell	LXFS660
	2.8	4,8	mammary	MX1
Comp. 1	>30.0	>30.0	[all]

4. In vivo experiments

Compounds of Example 6 and Reference Examples 1, 4, 8, 9 and 10 were subjected to in vivo testing in nude mice bearing subcutaneously growing human tumor xenograft LXFL 529. The indigoid bisindole derivatives were applied intraperitoneally to the animals in doses and according to the schedule as described in Table 4.

Table 4

	doses [mg/kg/day]	schedule of application [day(s)]	activity rating	Graph shown in Figure
Ex. 1 (Ref. Ex.)	100	1-5,8-9	+	Fg. 1 and 2
Ex. 1 (Ref. Ex.)	200	1-5,8-9	++	Fig. 1 and 2
Ex. 4 (Ref. Ex.)	100	1-5	++	Fig. 1 and 2
Ex. 4 (Ref. Ex.)	300	1-5	++	Fig. 1 and 2
Ex. 6 (Invention)	100	1-5,8-12,15,17,19,22	++	Fig. 1 and 2
Ex. 6 (Invention)	300	1,4,8,11,15,18,22	++	Fig. 3 and 4
Ex. 8 (Ref. Ex.)	100	1,4,8,11,15,18,22	-	Fig. 3 and 4
Ex. 8 (Ref. Ex.)	300	1,4,8,11,15,18,22	-	Fig.3 and 4
Ex. 9 (Ref. Ex.)	100	1,4,8,11,15,18,22	-	Fig. 3 and 4
Ex. 9 (Ref. Ex.)	300	1,4,8,11,15,18,22	+	Fig. 3 and 4
Ex.10 (Ref. Ex.)	30	1-5	-	Fig. 5 and 6
	100	1-5	-	Fig. 5 and 6
	300	1-5	+	Fig. 5 and 6
Ex.14 (Ref. Ex.)	10	1-5, 8-12	-	Fig. 7 and 8
	100	1-5. 8-12	+	Fig. 7 and 8
	300	3-5, 8-12	+	Fig. 7 and 8

The experiments were run for 21 or 28 days. Anti-tumor activity was evaluated comparing the median tumor volume relative to control, expressed as %T/C, wherein T is the test group and C the vehicle control group. In Table 4, anti-tumor activity is given according to an activity rate scale.

Activity rating:

-	inactive	T/C > 50 %
+	tumor inhibition	T/C > 25 - 50 %
++	tumor stasis	T/C ≤ 25 %

The results are further demonstrated by Figures 1 to 8.
A reduction of the body weight of the tested mice of more then 20 % by weight in general is interpreted as a toxic dose.

Claims

Use of a cell membrane penetrating indirubin derivative for the manufacture of a medicament for the treatment of human solid tumors and metastasis thereof wherein the indirubin derivative is selected from 5-methyl indirubin represented by the following formula (I):
wherein the solid tumors are selected from mammary carcinoma, melanoma, large-cell lung carcinoma, small-cell lung carcinoma, lung adenocarcinoma, colon carcinoma, bladder carcinoma, ovarian carcinoma, pancreatic carcinoma, renal carcinoma, prostatic carcinoma and melanomas.
Use according to claim 1, wherein the indirubin derivative is in the form of a physiologically acceptable salt.